A photodetector is a device, which measures the intensity of an incident photon beam by outputting an electrical signal proportional to the number of incident photons. A photodetector is sensitive to incident photons, provided that the photon energy is larger than the bandgap of the photodetector material. In a conventional setup, wavelength-sensitivity is achieved for example by using spectral filters in front of the photodetector, such that only photons in a limited spectral range are incident onto the photodetector. If these filters are produced on the photodetector substrate, the processing costs will be very high. It is also a research topic on its own to develop materials, which have a sharp pass/block transition around the desired wavelength. In addition, the minimum photon energy, which can be detected, is still determined by the photodetector material. Another way to achieve wavelength-sensitivity is to use a monochromator in front of the detector. The monochromator diffracts the incident photon beam and a grating then selects a particular (narrow) spectral range of the incident photon beam, which then is incident on the detector. By scanning the grating of the monochromator, the whole spectral density of the incident photon beam can be determined. At the same time, a monochromator often takes a lot of space and requires additional equipment to control the grating of the monochromator.
Nanocrystals (NC) and nanowires (NW) have attracted considerable attention nowadays due to the interesting fundamental properties present in such low-dimensional systems and the exciting prospects for utilizing these materials in nanotechnology-enabled electronic and photonic applications.
The photonic applications of nanowires is described in Gudiksen et al. (J. Phys. Chem. B 106, 4036, 2002), specifically, size-dependent photoluminescence from single indium phosphide nanowires. This publication presents the change in peak frequency of the photoluminescent spectrum of a nanowire, as the diameter of the nanowire varies. This effect is explained by radial quantum confinement of electrons and holes in the narrow nanowires. This publication mentions the possibility to use several materials and wires with different diameters simultaneously, but this is a conventional setup, which includes for example the use of a monochromator to determine the frequency of the incident light.
Wang et al. describes highly polarized photoluminescence from and polarization-sensitive photodetection with single indium phosphide nanowires (Science 293, 1455, 2001). This publication presents a horizontal nanowire used as a photoconductor, and demonstrates the sensitivity of the nanowire to the polarization of the incident light. Suggestions are made about the use of other materials for the nanowire.